Such saws are known and may include blades formed with integral teeth which are ground and set to particular requirements. These blades are suitable for wood and plastics but not for some manufactured materials such as chipboard. Blades are also known, for example from EP-A-0361875, which incorporate tungsten carbide teeth set in the blade. These are suitable for cutting such material as chipboard. Indeed this design has been found particularly effective because alternate facing teeth on each blade have chamfered faces firstly towards and secondly away from each other. Those teeth chamfered towards one another urge the two reciprocating blades together during their passage through the material being cut, (and themselves very effectively cut material by a scissor action as they pass one another) so that ingression of loose cut material between the blades is minimised; while those teeth chamfered away from one another rip out the inside of the groove being cut in the material so as to make room for the blade's passage through the material.
Although this design is very effective, even when they are employed for cutting such masonry products as breeze blocks and the like the life of the blade is nevertheless considerably shortened in this sort of environment. In the first place tooth breakage sometimes occurs and this may be caused for several reasons; for example, a tooth simply hitting, and fracturing on impact with, a particularly hard region of material being cut; or two teeth in scissor action crushing between them a particularly hard grain. In the second place, with such granular masonry material as breeze blocks and the like, excessive wear occurs between the teeth, particularly where the shape of the teeth causes them to be pressed together.
Thirdly, a possibly unrelated problem with the blades described in the above-mentioned specification is beginning to come to light, and which is probably caused by using the saw in such arduous conditions. This problem is that, with this construction, blades appear to be snapping on occasion adjacent their root in the saw. This again may be caused by teeth impacting hard regions and the blade buckling near its root where it is unsupported by the saw blade support guide.